1. Field of the Invention
This invention relates to a new and improved container closure and container neck structure and more particularly to a structure wherein the closure is applied with a single one-dimensional axial downward force onto the neck and is held in such position by a tamper-evident band. The consumer destroys a frangible connection between the cap and the band during initial removal, preferably by tearing away the band enabling the closure to be unscrewed from the container neck. When the cap is used for reclosure purposes, it may be screwed on and screwed off in the same manner as screw caps have heretofore been used.
2. Description of Related Art
Prior snap-on, screw-off structures may be classified under either of the following categories:
(1) Those with thread engagement as initially applied,
(2) Those without.
The major advantages of the no-thread initial engagement systems are that they are conceptually simple, careful alignment of the closure and the container is not necessary upon application of the closure, and easy (low force) application is possible since no thread-jumping is required. This version can be an aesthetically pleasing, straight wall cap design, and good re-seal is achieved on reclosure because of the torque advantage of threads. On the other hand, the disadvantages of such a system are that it may be confusing to the consumer because initial removal is merely by lifting the cap off the neck but subsequent use requires twisting the cap relative to the neck. Further, it is difficult to use the system with a lined closure because of the height relationships between the finish and the cap, and finally the cap must be relatively tall, which forces the use of fine threads, which can be difficult to mold. None of these disadvantages are present in this invention.
A closure such as Cresci U.S. Pat. No. 4,561,553 has a number of problems. The tamper evident feature of the closure may be circumvented by being able to engage the threads of the neck and closure (thereby creating a mechanical advantage) and back off the cap while the tamper-evident band is intact. Secondly, the device is confusing to the consumer since the cap is screwed off during removal only by inwardly distorting the cap skirt. The cap is reapplied as a standard snap cap.
Full thread engagement as the cap is initially applied has a number of conceptual advantages. Consumer confusion is eliminated since initial removal is by unscrewing. A number of seal systems, including foil, full liner, plugs or other linerless seals can be used. However, full engagement systems heretofore have been difficult to achieve in practice. A disadvantage of a closure such as Carr U.S. Pat. No. 4,625,875 is that there is no practical, consistent means to orient the cap relative to the container so that, after application, the cap must be turned at least slightly to ensure a tight seal. This defeats the purpose of a push-on cap. Also, the use of a stretch snap-band tamper evident ring excessively increases the application force necessary to seat the cap.
The present invention provides full thread engagement by reason of unique thread design and, more particularly, a unique tamper-evident band (i.e., lower skirt portion) attached to the upper part of the cap by multiple bridges or by means of a continuous line of weakness between the cap and tear band, as well as a means of orienting closure and bottle threads to achieve registration prior to straight axial application.
The present invention has considerable advantages over prior structures for the reasons above noted, among others.
The present invention comprises an improved closure or cap and an improved neck finish. The cap skirt and neck are provided with mating threads of such shape that the cap may be applied in a simple downward vertical movement, the cap skirt and neck flexing sufficiently to permit the threads to slip past each other.
The threads may be continuous or interrupted. Also, instead of there being two threadsxe2x80x94one on the neck and one on the cap, one external thread may be replaced with a groove. The term xe2x80x9chelical engagement meansxe2x80x9d is sometimes used herein to encompass all such screw retention means.
The cap has a tamper-evident tear band below the skirt which is connected to the skirt by a plurality of bridges or by a continuous line of weakness. Ratchet teeth are positioned on the inside of the tamper evident band. Correspondingly, the container neck below the threads is formed with external ratchet teeth. The mating ratchet teeth of the cap and container neck are engaged by the initial downward movement of the cap relative to the neck. In other words, in order to engage the ratchet teeth it is not necessary to rotate the cap relative to the neck, thereby differing from conventional threaded tamper-evident caps. It is merely necessary to provide alignment means on the cap and on the container so that the cap is initially properly oriented in such position that a direct single vertically downward movement of the cap relative to the neck causes the threads to slip relative to each other and the ratchet teeth to lock in final position. Chamfers on the ratchet structure of either closure or container can be used as a xe2x80x9cfinexe2x80x9d orientation system as the closure is initially applied.
To achieve proper registration of threads when a simple direct axial application force is used, both the neck threads and closure threads must be oriented. Orientation of the container is relatively easy. Generally, containers are either non-circular or have non-circular features which may be used for proper orientation. In accordance with a preferred form of the invention shown herein, the closure has a downward projecting tab similar to the tear tab used on push-on tear-off closures. The vertical tear tab characteristic of the present closure is an excellent orientation feature. However, other means for orienting the cap and container may be used.
Thread design is another feature of the invention. A large number of threads per inch of axial height is desirable for two reasons. First, a fine thread may be used and such a thread does not have to be as deep as a coarse thread, and hence the forces required for threads to jump during application are minimized. Secondly, fine threads minimize the height required to achieve a standard design criterion of 360xc2x0 or more of thread engagement which permits a lighter closure weight.
The greater the number of thread leads, the less actual turning action is required to remove or reapply the cap. In addition, multiple thread leads promote more xe2x80x9csquarenessxe2x80x9d during straight axial application. In other words, the cap seats horizontally on the neck because the termini of the threads are statically balanced. However, additional leads require a higher thread pitch assuming constant threads per inch and excessively high thread pitch results in a situation where the closure may back off or unscrew itself from sealed position.
In accordance with the present invention, a preferred thread for a blow-molded, high density polyethylene bottle is 12 threads per inch and two leads. If bottle finish processing permits, it would be advantageous to design for higher threads per inch and more leads. For example, if the bottle is made with injection blow mold equipment, a very fine bottle thread is possible. In that case, it might be preferable to use, for example, a 16 thread-per-inch, 4 lead, 4 pitch thread. The more leads, the more squarely the cap sets on the neck and the more effectively the closure will be seated by a direct downward, axial application force.
Also, consumer advantages of quick release and reapplication can be achieved with multiple lead threads.
In order to provide a tamper-evident feature, the closure should not be removable without some apparent closure characteristic changing. Generally, this requirement is satisfied by incorporating a frangible section which is destroyed during initial closure removal. One type of frangible section is a continuous thinned tear line, but in a cap of the present invention, such a system may not be the best choice, although permissible and is disclosed as a modification of the first embodiment of the invention. A preferred tamper-evident feature provides a frangible section having a number of frangible connections or bridges between the closure skirt and a tamper-evident ring below the bottom edge of the skirt. The preferred approach is to incorporate enough bridges around the circumference such that the combined strength of the bridges prevents unscrewing. The tamper evident band must be removed to allow unscrewing. Sequential breaking of the many bridges around the circumference simulates a continuous tear. A second approach is to incorporate only a few bridges around the circumference of the skirt such that the combined strength of the bridges is not sufficient to prevent unscrewing and the bridges rupture as the cap is initially unscrewed. With this second approach the broken bridges give evidence of opening. A major advantage of using bridges rather than a continuous tear strip is that a wide range of material choices is possible. Therefore a multiple bridge simulated tear structure is generally preferred over continuous tear frangible sections and this approach is used in the preferred embodiments of the present invention. However, in a modification of the invention an uninterrupted horizontal shoulder between the upper and lower portions of the cap is used, which shoulder is formed with a line of weakness. The alternative modification eliminates the space between the bridges to create a continuous frangible line. This modification is used successfully only when the cap is formed of a low density polyethylene and is not successfully used with higher density plastic materials. One of the advantages of the elimination of the spaced bridges is that of cleanliness in that the continuous shoulder prevents dirt and liquids from contacting any portion of the neck surface above the bottom edge of the cap.
In a preferred embodiment of the invention hereinafter described in detail, the closure is first oriented by means of its tear tab and the containers are likewise oriented. The closure and bottle are snapped together and the orientation allows registration of both the threads and the ratchets which hold the cap in place until the tamper-evident band is removed. Seal of the container may be made with a liner, foil or a linerless feature such as a plug or flap. Before initial removal, the multiple bridges are collectively sufficiently strong to prevent unscrewing and also resist any tendency of the closure to back off the neck. During initial removal, in the preferred embodiment the tear band is removed through sequential breaking of the bridges, thereby simulating a continuous tear strip but allowing the use of such plastic materials as polypropylene and high density polyethylene. Once the tear band is removed, the system functions as with normal threaded closures. Alternatively the upper and lower portions of the cap skirt are connected by a reduced number of angularly spaced bridges. Merely by twisting the upper skirt portion the bridges may be severed, giving evidence of tampering, and making it possible to unscrew the cap.
One of the features of the present invention is that the lower skirt portion, which includes tamper-evident features and, more particularly, contains ratchet teeth mating with corresponding teeth on the container neck, is formed with a vertical line of weakness and a tear tab adjacent thereto. When the lower skirt is removed it tears along the vertical line of weakness as well as along the line of weakness between the upper part of the cap and the lower skirt (i.e., tamper-evident band.) This feature has a number of advantages:
First, it prevents defeating the tamper-evident feature. Were it not for the vertical line of weakness, a dishonest patron might unscrew the upper cap, remove the contents of the container and replace the cap. It is somewhat difficult to observe that the line of weakness between the upper cap and tamper-evident band has been severed. When the vertical line of weakness is severed, this is not a problem since the lower skirt cannot be replaced.
Second, if the molds for the cap are not perfectly supported, plastic material may fill some or all of the voids between bridges joining the upper cap to the tamper-evident band. This makes it difficult for some users to remove the tamper-evident band. The vertical line of weakness makes it much easier to remove the lower skirt or band. Indeed, the bridges between the upper cap and band may be made thicker or some of the voids between bridges may be eliminated.
Thirdly, the intact tamper-evident band may create a danger to wildlife if the head of a bird, fish or small animal is entrapped therein. Splitting the band along the vertical line of weakness eliminates this hazard.
A further feature of the invention is the fact that the cap ratchet lug on the interior of the lower cap skirt is located between two external lugs on the neck finish when the cap is applied so that on application the cap cannot rotate outside of its xe2x80x9ctolerance rangexe2x80x9dxe2x80x94that is, there is an orientation feature of the cap and bottle ratchets for proper engagement.
Another advantage of the invention is that the cap may be applied to the neck in two stages (i.e., xe2x80x9cdouble clickxe2x80x9d). When the container is filled with milk or certain other liquids, entrapped air or other gases tend to cause foam. The thread structure of the present invention makes it possible to press the cap down until one set of threads passes the other. This holds the cap on the neck and holds it properly aligned relative to the neck ratchet. However, the cap is not tight and hence air and gas may escape. Then the cap is pressed down once more to tightly engaged and sealed position. To insure two xe2x80x9cclicksxe2x80x9d the closure thread has to jump two neck threads during application. This means that if the cap threads extend a full 360xc2x0 around the cap skirt inner wall (180xc2x0 each for double lead threads), the finish threads have to be repetitive at some point of the circumference. This also means that either the cap threads or the finish thread must be repetitive vertically. I.e., the threads must overlap on either the neck or cap in order to make possible the double click.
More specifically, the caps pass down a conveyor overlying the path of the containers and as each container passes the end of the conveyor, a cap drops onto the neck. The cap and neck then pass under a roller which preliminarily presses the cap down on the neck. One of the features of the thread construction of the present invention is that there is more than one full turn of thread engagement of the threads. Hence, the roller pushing the cap through the first step or snap prevents the latter from falling off the neck when it is subjected to such action as milk foaming in the interior of the container. Hence the cap stays on the bottle, although not being tightly sealed thereto, until the bottle passes under the conventional capping machine belt or pressure plate which fully seats the cap on the neck. This is a second step or snap of the cap on the bottle and insures that both threads are tightly engaged.
When the first snap of the cap on the bottle occurs, the ratchet teeth of the cap engage the ratchet teeth of the neck but a slight twisting is possible within the range of tolerance of approximately 20 degrees. Such a rotation of the cap relative to the neck changes the height of the cap only about 0.009 inches. However, this turning ability of the cap relative to the neck with such slight changes in the height of the cap relative to the neck insures proper final alignment of the ratchet teeth of the cap and neck, while permitting release of foam or excess air.
Still another feature of the invention is an internal shoulder at the intersection of the underside of the disk and the top of the upper cap skirt. This shoulder prevents the cap from being turned or torqued to jump threads or strip the threads. The inner plug of the cap tends to push the neck of the bottle outward against the shoulder and the shoulder then prevents turning or stripping. Further, the fit of the shoulder against the neck tends to reduce leakage and rigidities the cap.
Another feature of the present invention is that the cap is provided with a plug or inner skirt which fits inside the bottle neck. The length of this plug is related to the positioning of the screw threads on the cap in such manner that the threads of the cap and bottle neck engage before the plug engages the neck. Thus a quarter-turn of each of the double lead threads occurs before the plug contacts the neck. This feature reduces the possibility of cross-threading when the cap is applied to the neck as a reclosure cap.